Always use fake keycode bindings for level3 and level5

Always use fake keycode bindings for level3 and level5

With this patch the real modifiers get bound to a virtual modifier only
through fake keycodes, which accounts for both the case where a key gets
bound to a different modifier by the first layout (and thus the second
layout loses its modifier behaviour) and the case where two virtual
modifiers would get bound to the same keycode.

see bug report #50935